AlSi10Mg alloy products with a hydrogen content of approximately 3.9 or 5.6 cm3 /100g–Al of hydrogen were fabricated by selective laser melting (SLM)
using normal (as–received) and moist powders, and their non–reversible dimensional changes during heat treatment at 473 or 803 K were investigated. The linear
dimensional change arising from the heat treatment at 473 K was approximately 0.22ÿ by 3.6 ks and remained constant thereafter. This behavior was independent
of the amount of hydrogen in the SLM products, suggesting that the dimensional changes at 473 K were induced by precipitation of Si phase from the ÿ–Al phase.
However, the linear dimensional changes during the heat treatment at 803 K were comparatively large and continued to increase during the heat treatment. At the
same time, the linear dimensional changes at 803 K also showed a dependence on the amount of hydrogen in the SLM products. These phenomena indicated that
the porosity expansion and precipitation of Si phase occurred simultaneously at 803 K. For the SLM product with a hydrogen content of approximately 3.9 cm3 /
100g–Al, the linear dimensional change during the heat treatment at 803 K was 0.867ÿ at 18 ks, of which 0.116ÿ and 0.751ÿ were estimated to have been induced
by the precipitation of Si phase and the porosity expansion, respectively. From gas analyses using different methods, it was elucidated that the hydrogen desorbed
from the powder and was entrapped in the SLM products at the time of laser scanning, and then enriched to the porosities during the heat treatment at 803 K,
causing the porosity expansion.